Free piston engine starter



R. F. FALBERG 2,956,396

Oct. 18, 1960 FREE PISTON ENGINE STARTER 3 Sheets-Sheet 1 Filed Nov. *1, 1956 IN VEN TOR.

Oct. 18, 1960 R. F. FALBERG 2,956,395

FREE PISTON ENGINE STARTER Filed Nov. 7, 1956 3 Sheets-Sheet 2 IN VEN TOR.

A TT'OPNE'Y Oct. 18, 1960 R. F. FALBERG 2,956,396

FREE PISTON ENGINE STARTER Filed Nov. 7, 1956 3 Sheets-Sheet 3 INVENTOR.

ATTORNEY United States Patent FREE PISTON ENGINE STARTER Robert F. Falberg, Birmingham, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Nov. 7, 1956, Ser. No. 620,972

'9 Claims. (CI. 60-14) This invention relates to starting free piston engines, 'gasifiers, or compressors. The invention relates more particularly to automatic starting of free piston machines using an automatic sequential starting cycle and to the devices used for controlling the timing and positioning of elements of the starting system.

Free piston machines require relatively complex starting mechanisms compared to the simple starting devices used in piston type internal combustion engines wherein the pistons are mechanically connected to each other and to the output shaft. Certain operations such as moving the pistons to their outer positions, holding them in this position while providing a build up of pressure on the pistons, and subsequently releasing the holding means to allow the pressure to move the pistons inward, require accurate timing and positioning devices in order that these steps be performed in proper sequence. Heretofore, electrical solenoids, relays and solenoid operated valves as well as manual controls have been utilized to perform these functions. Electrically reversible motor driven pumps have been used for creating the force necessary to perform steps during the starting procedure. These electrical components generally are expensive, bulky and require considerable space. Furthermore, complex electrical systems require considerable maintenance.

It is therefore an object of this invention to provide a system employing a unidirectional starting pump for positioning the motor and compressor pistons during the starting cycle.

An additional object is to provide a simple mechanically operated device to control the sequential events of the starting cycle of a free piston machine.

These and other objects and advantages of the invention will be readily apparent from the following specification and drawings which illustrate a preferred embodiment of the invention but which are not to be considered as limiting the invention.

The preferred embodiment of the invention comprises a unidirectional air pump that is alternatively connected to create a vacuum in the cushion chambers of the free piston machine and pull the pistons to their outer position, or connected to create a positive pressure in the chambers to push the pistons to their inner position. The alternative actions depend on the position of a control valve that alternatively connects the pump intake or supply to the cushion chambers. This control valve is initially moved between its evacuating and pressurizing positions by the pistons themselves and then by a spring urged piston acting on the valve through a cam device. The control valve is held in its pressurizing position by a latch mechanism until air pressure from air spring piston has returned to its original position. Initial movement of the control valve from itts vacuuming position to its pressurizing position is accomplished mechanically by the engine pistons themselves. The latch means that holds the pistons in their outer positions during the startice 2 ing cycle is also operated and controlled by fluidpressure in the system. 7

Referring to the drawings:

Figure l is a diagrammatic sectional View of a dual free piston machine;

Figure 2 illustrates schematically a portion of the starter control system for the free piston machine of Figure 1 in one condition of operation; and

Figure 3 illustrates the starter system in another condition of operation.

Figure l ofv the drawings diagrammatically shows a dual unit free'piston machine that could be used as a gasifier for providing a continuous supply of gases under high pressure and temperature to a prime mover such as a gas turbine, although the machine could be adapted for use as a gas compressor or other purposes than as a gasifier for a turbine.

The engine includes a case or housing 1, a portion of which defines two motor cylinders 2 in which are reciprocably mounted opposed mot-or pistons 3. Each motor cylinder 2 has inlet ports 4 and exhaust ports 5 at opposite ends of the cylinder. These ports are opened and closed by the motor pistons 3 which are rigid with large compressor pistons 6 that are mounted for reciprocation in the compressor cylinders 7 also formed as part of the engine case 1. Each compressor cylinder has an inlet port 8 controlled by a valve 9 urged to its closed position by spring 10, and an exhaust port 11 controlled by a valve 12 urged to its closed position by a spring 13. The opposed movable masses of the pistons 3 and 6 of each unit are kept in proper relationship with each other by a separate synchronizing linkage 14 for each unit, which may be of known type. The individual units are designated by A and B in Fig. 1. It is to be understood that a single unit machine may also be utilized in the invention.

The two units of the engine are operated on a known supercharged two stroke diesel engine principle. Initial movement of the movable masses 3-6 towards each other causes entrapment of supercharged air and further compression of the air in the motor cylinders 2. At the proper time, fuel is injected by suitable means (not shown) into the compressed air between the motor pistons and is ignited by the heat of compression. The increase in pressure created by the burning fuel acts on the opposed faces of the motor pistons 3 and forces the movable masses 36 away from each other.

The compressor cylinder 7 is divided by the compressor piston 6 into a compression chamber 16 and a cushion or bounce chamber 17. When the movable masses 3-6 are moved outward, their outward motion is checked by air trapped in the pneumatic cushion chamber 17, which then possesses practically all of the energy developed by the motor cylinder 2 and restores this energy to the movable masses 36 during the next inward stroke. The motor cylinder 2 is scavenged by air drawn in through the inlet valves 9 during outward movement of the masses 3-6, compressed in chamber 16 during the inward stroke of the masses 36, and delivered through the discharge valves 12 into the case chamber 18. A connecting passage 19 provides for equalizing the pressure in the two case chambers 18. On the next outward stroke of the masses 36 the air under pressure in the case chamber 18 enters the motor cylinder 2 through inlet port 4 and travels through the motor cylinder 2 and out exhaust ports 5 into the exhaust collector 63 and then to some power generating device such as a gas turbine.

The cushion chambers 17 of each unit are connected together by suitable means 68 to balance the pressures in the opposite chambers. The pressure in the chambers after starting is controlled by a stabilizer S which is of known type, such as those shown in US. Patent No. 2,355,924. The stabilizer which forms no part of this invention operates only after the starting cycle is completed. g

The two units A and B would normally be connected together by conduit 66 through a normally open isolating valve I such as that shown in application U.S. Ser. No. 584,744 to Warren H. Smith, filed May 14, 1956, now Patent No. 2,839,911, issued June 24, 1958. This valve would operate to isolate the chambers after starting when a depl'laser D, which may be of known type such as those described in U.S. Patent No. 2,473,204, would act to vary the speed of one unit relative to the other until the pistons of one unit are approximately at, the inner dead center when the pistons of the other unit are at outer dead center. The isolating valve, stabilizer and dephaser are described in the application and patents referred to and the detailsare immaterial {to this invention and, hence, are not described. The starting control shown in Figs. 2 and 3 is connected to the machine at conduit 26.

Figs. 2 and 3 show the portion of the control system used to maneuver the opposed masses 36 during the starting operation; The controls consist primarily of: 1) a unidirectional air pump; (2) synchronizer linkages 14 and a latch mechanism 20; "and (3) a maneuvering control valve generally indicated at 30. Briefly, the starting cy'cl'eisas follows: 1) the movable masses 36 are moved outward by the creation of a vacuum in the cushion chambers 17; (2) a latching mechanism is then moved into the return path of the linkages 14 connected to the masses 3-6; (3) a positive pressure is then introduced into the cushion chambers17 to move the masses 3-6 inward until stopped by the latch mechanism; (4) the pressure in chambers 17 is built up to a predetermined level; and (5) the latch mechanism releases the movable masses 3-6, allowing the compressed air in the chamber 17 to force the movable masses in towards each other. The synchronizing and latching mechanisms 14 and 20 include a link 21 secured to a shaft 22 having on either end a latch member 23 which can be rotated into the path of an arm 24 pivotally mounted on a fixed pivot 25. The arm 24 of each unit has its opposite ends connected by linkage to the opposed compressor pistons 6 of that unit. In the holding position (Fig. 2) of the latch mechanism, the latch 23 is in the path of the arm 24 so that when air pressure is introduced into chambers 17, pressure acts'on the movable mass 36 to move the same slowly inward until the arm 24 engages the latch 23. Pressure in the chamber 17 then rises to a predetermined level, whereupon the controls cause movement of piston 27 of the latch mechanism 20 to rapidly move the linkage 21. This rotates the shaft 22 and latch 23 to the position shown in Fig. 3, thereby releasing the movable masses 3- 6 and allowing the air under pressure in the chamber 17 to move the movable masses 3-6 rapidly inward.

To control the movement of piston 27 which operates the latch 23 and to alternate the connections between a pump 45 and chamber 17, there is provided a positioning control valve assembly indicated at 30. This valve assembly consists of a valve body 31 enclosing a spool valve member 32 having four lands 32a, 32b, 32c and 32 1. The valve body 31 is connected to the pump through passages 46 and 47, to the latch control mechanism by passage 60, to the engine cushion chambers by passage 51, and to the atmosphere through passages 54, 62 and vents 52. Formed on a portion of the valve member 32 extending through the casing 31 is an enlarged bifurcated section 65 having an inclined cam surface 33 and an adjacent fiat surface 33a. A cam follower 34 having a cam roller 34a is reciprocably mounted in a housing or chamber 38 attached to valve body 31 for cooperation with the surfaces 33 and 33a. The portion 65 of the valve member 32 carried outside the casing31'has a latchmember35 pivotally connected thereto by a pin 35a. As shown in Fig. 2, this latch 35 is urged to its upper position by a spring 36. The cam follower 34 is normally urged downward as viewed in the figures by a spring 37 contained within the cam follower chamber 38. A valve spring 39 continuously acts between the left hand end of the valve casing 31 and land 32a of the valve member to urge it to its right hand or evacuating position. The left hand end of the valve 32 is connected to a balance arm 40 by a pin 41. As seen in Fig. 1 the opposite ends of the balance arm 40 are disposed in the path of push rods 42 that have heads 43 formed thereon adapted to engage the opposite ends of the balance arm 40. These push rods are normally urged outward by springs 44. The push rods 42 extend into the compression cylinder 7 and are adapted to be engaged and moved by the compressor piston 6 at the close of the outward movement of the pistons during the starting cycle, but are not engaged by the pistons during the normal operating stroke of the pistons when trapped air in the chambers 17 limits outward movement of the pistons 6.

The piston maneuvering and controlling 'fiuid pressures are produced by a fluid pump schematically indicated at 45. This pump may be driven by any suitable means such as an electric motor, air motor or other device and has an intake passage 46 and a supply passage 47. The pump passages 46 and 47 are connected into the control valve body 31. A passage 51 extends from the valve body 31 to a passage 26 through a chamber 48 in which a check valve 49 is urged by a spring 50 t'o'close the conduit '51 from communication with the passage 26. Passage 26 is connected to the cushion chambers 17 of the free piston engine. When energized, the pump '45 acts either to create a vacuum in the cushion chamber 17 or to create a pressure in that chamber, depending on the position of the control valve 32. The valve 32 in Fig.2 is shown connecting the pump for pressurizing the chamber 17 and in Fig. 3 for evacuating the chamber 17. v

In the vacuumizing or normal position of Fig. 3 the cam follower 34 is in the upper portion of its'stroke and the roller 34a is in contact with surface 33a, with the spring 39 maintaining the valve 32 in'its right hand position. Upon operation of the pump 45 air is withdrawn from chambers 17 through the passage 26, check valve 49, passage 51, between lands 32a and 32b of the valve member 32, through intake passage 46, and into'the pump 45. The air is then forced out line 47 through the'valve body'31 and to the atmosphere through vents 52. This'eva'cu'ating of chamber 17 causes the'movable masses 3--6 to move towards its outwardmost position until the compressor pistons 6 engage push rods 42 (seeFig. 1). Further movement of the compressor pistons 6 causes enough movement of the push rods 42 'and, consequently, balance arm 40 to move the valve 32-slightly to the left-as viewed in the figures. This movement of the valve 32'is sufiicient to allow the push rod roller 34a to be moved'from a position of rest on surface 33a to'a position onthe c'am surface 33. The force of the cam follower spring 37 imparted to the push rod roller 34a forces the spool valve 32 to move rapidly to the left by imparting'a resultant force to the left on the cam 43. During its movement down cam 33, the push rod roller'34a depresses the'latch 35 which rotates about its pin 35a. When the 'cam roller 34a reaches the bottom of the cam 33, the'latch spring 36 returns the latch to its normalposition-as shown in Fig. 2.

Movement of the control valve 32'to the left has connected the pump 45 so that it forces air under pressure into chamber 53 of the latch releasing mechanism and, subsequently, into chamber 17. This action occurs as follows: Referring to Fig. 2 which shows the valve at its pressu-rizing'position, air is drawn from passage 54 into the valve body 31, through a bore 55 in the valve member 32, a port 56 betweenlands 32b and-32c, into pump intake passage 46, through the pump 45 and into passage 47, through the control valve between lands 32a and 32b, and through passage 51. Pressure in passage 51 first acts to close the check valve 49 and at the same time opens a check valve 57 against the spring 58 and passes into line 59, through the valve body 31 between lands 32c and 32d, into the line 60 which leads into chamber 53 of the latch releasing mechanism. The air under pressure in chamber 53 moves piston 27 to the left against spring 64 and through the linkage 28, 29 and 21, rotates the shaft 22 and the latches 23 to the locking position as shown in Fig. 2. Near the end of its movement to the left the piston 27 pushes the check valve 49 oif its seat, allowing air under pressure in line 51 to pass to line 26 and into the chamber 17.

As the air pressure in the cushion chamber 17 gradually builds up, the movable masses 36 move slowly to their inner position until the arms 24 of the synchronizing linkages 14 engage the latches 23. Pressure then continues to build up in chamber 17 until the pressure acting through passage 61 on the lower surface of the cam follower piston 34 moves the piston 34 against the spring 37. The valve 32 remains stationary during this upward movement of the cam follower 34 because the cam follower roller 34a follows the contour of the latch 35, which is held against the roller 34a by the spring force of return spring 39. When the cam follower roller 34a reaches the top of the latch 35 the latch 35 is depressed slightly against spring 36 allowing the spring 39 to return the valve 32 to the position shown in Fig. 3, the follower roller 34a returning to its normal position also. The rapid movement of valve 32 to the right (Figure 3) connects the chamber 53 of the latch control mechanism and passage 60 to the atmosphere through valve body 31 between passages 32c and 32d and exhaust passage 62. With the drop in pressure in chamber 53 the spring 64 moves the linkage 28, 29, 21, shaft 22 and latches 23 unlocking the synchronizer linkages and allowing the pressure in chambers 17 to start a rapid inward movement of the masses 36 for the first firing stroke.

After the compressor piston 6 and motor pistons 3 reach a predetermined inner position fuel is injected into the cylinder 2 and the engine operates under its own power. After the engine starts the pump 45 ceases operation and other controls, not shown, operate to regulate the pressure in cushion chamber 17, and to dephase the two free piston units so that a continuous supply of controlled gases under high pressure and temperature are supplied through the exhaust collector 63 to the gas turbine. These controls as well as the gas turbine have not been shown as they form no part of the invention as any form of free piston machine control could be utilized in a machine using the starting system of the present invention.

The operation of the starting system may be briefly summarized as follows: Initially the latch control mechanism 20 and positioning control valve 30 are positioned as shown in Figure 3. The pump 45 is operated whereby air is withdrawn from cushion chamber 17 through passage 26, check valve 49, line 1, between lands 32a and 32b of valve 32, through passage 46 and the pump into line 47, then through the valve body and out vent ports 52. When the pistons 6 reach the outer part of their stroke they engage push rods 42 causing balance arm 40 to move the valve 32 to a position where the cam follower roller 34a engages inclined cam surface 33 and allowing the force of spring 37, which acts through the cam follower 34, to force the valve 32 to the left against spring 39. Movement of valve 32 to the left causes cam follower 34 to move the latch 35 against the spring 36 and when the valve reaches the end of its stroke, Figure 2, the latch is returned by the spring 36 to its upper position blocking movement of the valve 32 to the right.

'. With the control valve as shown in Figure 2, pump 45 is now connected to draw air through ports 62 or 54 and passage 46 and will force it under pressure through line 47 into passage 51. Pressure in passage 51 acts to close the check valve 49 and also passes through check valve 57, line 59, through the valve 30, line 60 and into chamber 53 where it acts on piston 27 to move the links 28, 29, and 21 against the force of spring 64 to rotate shaft 22 and latch 23 to a blocking position. When the piston 27 has reached the end of its stroke to the leftas viewed in the figure it pushes check valve 49 off its seat allowing pressure in line 51 to pass into line 26 and into the cushion chamber 17. The pressure in chamber 17 then moves the pistons 6 inward until the synchroni'zer arm 24 contacts the latch 23. The pressure in chamber, 17 continues to rise and is transmitted through line 61 to act to move the cam follower 34 upward against the force of spring 37, the cam follower 34a meanwhile following the contour of latch 35. When cam follower 34 reaches the upper portion of its stroke, latch 35 is slightly depressed allowing spring 39 to rapidly move valve 32 to the Fig. 3 position, whereupon pressure in chamber 53 acting to hold the latching mechanism in its locking position escapes through passage 60, between lands 32c and 32d and exhaust passage 62. Spring 64 then moves linkage 28, 29 and 21 to move the latch 23 out of the path of linkage arm 24 and allows air under pressure in chamber 17 to rapidly move the pistons 6 inward toward their first firing stroke. The fuel is then injected into combustion chamber 15 and the movable masses 36 forced outward, their outward stroke being limited by air trapped in chamber 17. The continued operation of the free piston machine is then controlled in any known manner as by the stabilizer, dephaser and other controls.

The invention provides an improved control apparatus suitable for use in many applications in the art of free piston machine control and the principles of the invention may easily be utilized in other arts through the use of ordinary skill.

It will be apparent to those skilled in the art that many modifications of the system and components thereof may be made within the scope of the invention which is not to be considered as limited by the detailed description of the embodiment shown.

I claim:

1. In a starting system for a free piston engine having at least one power cylinder and one compressor cylinder interconnected together, at least one power piston and one compressor piston interconnected together and movable in said respective cylinders, said compressor cylinder and compressor piston forming a variable volume chamber, the combination of a fluid pump, suction and discharge passages for said pump, a two-position valve for alternatively connecting said suction and discharge passages with said chamber, and means for moving said valve between its two positions.

2. In a starting system for a free piston engine having at least one power cylinder and one compressor cylinder interconnected together, at least one power piston and one compressor piston interconnected together and movable in said respective cylinders, said compressor cylinder and compressor piston forming a variable volume chamber, the combination of a fluid pump, suction and discharge passages for said pump, a two-position valve for alternatively connecting said suction and discharge passages with said chamber, actuating means for moving said valve between its positions including means controlled by the position of said piston for initiating movement of the valve from a first position connecting said suction passage to said chamber toward a second position connecting said discharge passage to said cham her, and means for completing movement of said valve to said second position responsive to said initiating movement.

3. In a starting system for a free piston engine having at least one power cylinder and one compressor cylinder interconnected together, at least one power piston and one compressor piston interconnected together and movable in said respective cylinders, said compressor cylinder and compressor piston forming a variable volume. chambexg'the combination of a fluid pump, suction and discharge passages for .said pump, a two-position valve for alternatively connecting said suction and discharge passages with said chamber, first means for normally biasing said valve to connect said suction passage to said chamber, a second biasing'means stronger than the first biasing means for at. times moving said valve to con nect said discharge passage with said chamber, and means forrendering said second biasing means effective, said last-mentioned means being controlled by the position of the piston.

4. In a starting system for a free piston engine having atleast one power cylinder and one compressor cylinder interconnected together, at least one power piston and one compressor piston interconnected together and movable in said respective cylinders,said compressor cylinder and compressor piston forming a variable volume chamber, the combination of a fluid pump having suction and discharge passages, a two-way valve for alternatively connecting the suction or discharge passage to said chamber, said valve normally being positioned to connect said suction passage to said chamber and upon operation of the pump to cause reduction of pressure in said chamber, means controlled by the piston position for alternatively positioning said valve to connect said discharge passage to the chamber, and means controlled by'the pressure in said chamber for causing said valve to return to its normal position.

5. In a starting system for a free piston engine having at least one power cylinder and one compressor cylinder interconnected together, at least one power piston and one compressor piston interconnected together and movable in said respective cylinders, said compressor cylinder and compressor piston forming a variable volume chamber, the combination of a fluid pump having suction and discharge passages, a two-way valve for alternatively connecting the suction or discharge passage to said chamber, said valve normally biased to a position connecting said suction passage to said chamber and upon operation of the pump to cause reduction of pressure in said chamber, means controlled by the piston position for alternativelypositioning said valve to connect said discharge passage to the chamber, holding means for maintaining said valve in said alternative position, and means controlled by the pressure in said chamber for releasing said holding means and thereby allowing said valve to return to its normal position.

-6. In a free piston machinehaving an interconnected power cylinder and a compressor cylinder, interconnected power and compressor pistons in said respective cylinders each adapted to be moved between an inner and an outer position in said cylinders, a chamber formed by said compressor piston and compressorcylinder, and a conduit connected to said chamber, the combination'of a pump having suction and pressure passages, a valve having a first position for connecting said suction passage with said conduit for moving said compressor pistonto its outer position and a second position for connecting said pressure passage with said conduit for moving said compressor piston toward its inner position,.first valve actuating means responsive to movement of the compressor'piston to its outer position for moving said valve to its second position, second valve actuating means responsive to a predetermined positive pressure in said chamber for returning said valve to its first position, latch means responsive to movement of said valve to its second position for limiting movement of'said compressor piston from its outer to its inner "position and re sponsive to return of said valve to its first position for releasing said compressor piston for movement from its outer to its inner position.

7. In a starting system for a free piston engine having at least one ,power cylinder and one compressorcylinder interconnected together, at least one powerpiston and one compressor piston interconnected together and movable in said respective cylinders, said compressor cylinder and compressor ,piston forming a variable volume chamber, the combination of a fluid pump, suction and discharge passages for said pump, a two-position valve for alternatively connecting'said suction and'discharge passages with said chamber, actuating means for movingsaid valve between its positions including mechanical means controlled by the position of said piston and connected to said valve .for initiating movement of the same from a first position connecting said suction passage to said chamber toward a second position connecting said discharge passage to said chamber, and biasing means for completing movement of said valve to said second position responsive to said initiating movement.

8. In a starting system for a free piston engine having at least one power cylinder and one compressor cylinder interconnected together, at least one power piston and one compressor piston interconnected together and movable in said respective cylinders, said compressor cylinder and compressor piston forming a variable volume chamber, the combination .of a fluid pump having suction and discharge passages, a two-way valve for alternatively connecting the suction of discharge passage to said chamber, said valve normally biased to a position connecting said suction passage to said chamber and upon operation of the pump to cause reduction of pressure in said chamber, mechanical force applying means controlled by the piston position for alternatively positioning said valve to connect said discharge passage to the chamber, mechanical holding means for maintaining said valve in said alternative position, and fluid pressure responsive means controlled by the pressure of said chamber for releasing said holding means and thereby allowing said valve to return to its normal position.

9. In a free piston machine having an interconnected power cylinder and a compressor cylinder, interconnected power and compressor pistons in said respective cylinders each adapted to be moved between an inner and an outer position in said cylinders, a chamber formed by said compressor piston and compressor cylinder, and a conduit connected to said chamber, the combination of a pump having suction and pressure passages, a valve having a first position for connecting said suction passage with said conduit for moving said compressor piston to its outer position and a second position for connecting said pressure passage with said conduit for moving said compressor piston toward its inner position, first mechanical valve actuating means including spring biasing means responsive to movement of the compressor piston to its outer position for moving said valve to its second position, a valve latch for holding said valve in its second position, second valve actuating means including spring biasing means urging said valve to its first position and valve latch releasing means responsive to a predetermined positive pressure in said chamber for returning said valve to its first position, piston latch means responsive to movement of said valve to its second position for limiting movement of said compressor piston from its outer to its inner position and responsive to return'of said valve to its first position for releasing said compressor piston for movement from its outer to its inner position.

References Cited in the file of this patent UNITED STATES PATENTS 2,104,502 Allen Jan. 4, 1938 2,439,453 Cooper Apr. 13, 1948 2,473,204 Huber June 14, 1949 2,641,438 Arnold June 9, 1953 2,731,793 Lewis Jan. 24, 1956 2,795,927 Huber lune 18, 1957 

